Control system for electric motors.



1.5. LINEBAUGIL CONTROL SYSTEM FOR ELECTRIC MOTORS, APPLICATION FILEDJULY 30. 1914.

1,250,906. I Patented Dec. 18, 1917.

UNITED STATES rarnnr neuron JESSE J. LINEB AUGI-I, OF SCHENECTADY, NEWYORK, ASSIGNOB TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

CONTROL sYsTEM FOR ELECTRIC MOTORS.

Specification of Letters Patent.

Patented Dec. is, rem.

Application filed July 30, 1914. Serial No. 85%,074.

To all whom it may concern:

Be it known that I, Jnssu J. LINEBAUGH, a citizen of the United States,residing at Schenectady, county of Schenectady, State of New York, haveinvented certain new and useful Improvements in Control Systems forElectric Motors, of which the following is a specification.

My invention relates to the control of electric motors and has for itsobject the provision of improved means whereby an electric motor may bestarted, stopped andgenerally controlled in a reliable, safe andefiicient manner.

More specifically, my invention relates to the control of direct currentmotors, one of the objects being to provide improved means whereby anelectric motor may be retarded by causing it to act as a generator toreturn energy to the line. While my invention may be of generalapplication in the field of motor control, it is particularly applicableto electric traction systems. In the operation of trains on heavygrades, one of the great problems is the braking of the train. In someinstances on long grades, brake shoes will be worn out or destroyed in asingle trip. The Wear on the rails is also a matter of seriousconsideration. Furthermore, trouble is oftentimes caused b theoverheating which results from the raking. It has heretofore beenproposed to brake electrically operated trains at least in part bycausing the motors to act as generators and return energy to the line.This form of braking is commonly known as regenerative braking. One ofthedifiiculties, however, with using the system in electric traction isthat series motors are used almost universally in traction work and thecharacteristics of the series motors are not satisfactory forregenerative braking because of the well known variable fieldexcitation. 1n order to' overcome this difiiculty, it has heretofore thenecessary source of variable potential for imposing a controllableexcitation upon the series motors by a suitable source of power, such asa motor generator. The motor of the motor generator is connected tooperate on line potential, and the generator, which may be called theexciter, is connected across the fields of the motors, to give them astable characteristic. The field of the exciter is separately excitedfrom an auxiliary generator which may be used also for supplying thenecessary low voltage for the control circuit, lighting circuits, etc.Both the generator and the exciter may be driven by the same motor. Thevoltage of the exciter is varied so as to vary the excitation of thefields of the traction motorsby an automatic regulator under the controlof a contact making ammeter. One satisfactory means for accomplishingthis automatic variation is by means of a motor operated rheostat whichvaries the resistance in the exciter field, the operation of which iscon trolled by a contact-making ammeter in the regenerative brakingcircuit. By this arrangemcnt, if the braking current starts to riseabove a safe or desired value, theregnlator will operate to insertresistance in the field of the exciter and thereby lower the voltageimpressed on the motor fields, the effect of which will be to'lowcr thearmature voltage and thereby the braking current, or if the current istoo low, the regulator will operate to cut out resistance and increasethe braking current. The braking current will thus be kept practicallyconstant at the desired value regardless of variations of voltage,changes of grade and train friction. Furthermore, the saving of power .obraking position.

important. From ten to fifteen per cent. saving of power is quitecommon, and under some special conditions there will be-a much greatersaving. Means are also provided whereby the braking circuit cannot beclosed if there is any considerable difference be: tween. the linevoltage and the voltage of the motors acting as generators. This willprevent the too sudden application of a large braking effort which wouldjar the train and perhaps cause other damage. Means are also providedwhereby the operator may vary the braking effort at will and hetherefore always knows just what braking effort he will get when hethrows In other words, the braking is entirely within his control andtherg is no possibility of getting excessive cifircnts due to abnormalvariations of voltage or other causes. Other objects and features of myinvention will appear in the course of the following specification, in

which I have shown my invention embodied in concrete form for purposesof illustration.

My inventionwill be more readily under-.

stood by referring to the accompanying drawings, in which I have showndiagrammatically a motor control system embodying my improvements.

Referring to the drawing, it will be seen that I have shown my inventionin connection with an electric traction system which may be used eitheron a locomotive or on a. multiple unit system of control. In thisparticular case the system is intended for a locomotive having fourmotors controlled by series parallel control. Since my invention is inno wise limited in its application to any particular form of motorcontrol, I have merely shown motoring connections diagrammaticallywithout any attempt to illustrate the 'letail'connections involved inthe various steps of the control. The fields F of the four motors areconnected on the ground side of the armatures A and the motors arecaused to assume the various connections involved in series-parallelcontrol by means of contactors located in the contactor box 10, whichbox is broken away to show one of the cont-actors, a line contactor, 11.These'contactors are controlled in the w ell known manner by the mastercontroller 12, the control circuits for the cmitactors being carried inthe cable 13. Since the voltage on which a system of this characterwould ordinarily be used is high, the control circuit for the motors issupplied from the generator 14. This generator may supply any other lowvoltage circuits required in addition to the control circuit.

In order to superimpose a suitable potential upon the series fields l!of the motors for regenerative braking, I provide an exciting generatordriven by a series motor 16 connected to trolley T. This motor 16 in thepresent instance also drives the auxiliary generator 14, as wellas ablower for cooling the motors, although of course it will be perfectlyfeasible to have the various parts driven by other motors if desired.The armature of the exciter 15 is connected across the fields F of themotors through the wires 17 1S and 18, this circuit being controlled bythe contactor 19. In order to vary the excitation imposed upon thefields F, the exciter 15 has a separately excited field which, in thiscase, is supplied from the auxiliary generator 1 1. The potential of theexciter is controlled by varying the re-.

sistance 20 in the exciter field 21. This resistance 20 in the field ofthe exciter is controlled automatically by the motor cur- There arevarious ways of accomplishing this automatic control-but a veryeffective arrange 'ment is'shown in the drawings consisting with voltagefrom the generator 1-1. This motor is constantly operating, but willdrive nothing but the shaft 23 unless one of the clutches 24 or isthrown in. If the clutch 24 is thrown in, the rheostat arm will beoperated to cut in resistance, whereas if the clutch 25 is thrown in therheostat arm will be operated to cut out resistance in the exciter fieldcircuit 21. These clutches I have shown as being electrically operatedby means of solenoids 26 and 27 respectively, the circuits of which arecontrolled by a contactmaking ammeter C which is diagrammaticallyillustrated as consisting of a pivoted arm 28 operated by a solenoid 29arranged to move between contacts 30 and 31, the arrangement being suchthat when the arm engages the contact 30, solenoid 27 will be energizedfrom the generator 14, and when the contact 31 is engaged the solenoid26 will be similarly energized. As shown, the arm 28 is moved in onedirection by the spring 32 which acts in opposition to the solenoid 29.And this solenoid is energized in proportion'to the current duringregenerative braking, and to this end is connected across the resistance33, more 'or less of which is placed in circuit by the brakingcontroller during regenerative braking.

A switch is provided for changing the connection from motoring tobraking. The motoring connection established by this switch simplyconsists of bridging the contacls 36 which closes the line contactor 11and completes the motor circuit. WVhen the switch is thrown to thebraking position two things are done: first, the contactor 19 is..closod which connects the exciter 15 across the field coils F; second,the line contactor 11 is energized in part through a different i of linecontactor 11.

circuit than it was on the motor side. It is now energized through wire37 and contacts 38. These contacts 38 form part of differential voltagerelay R which is responsive to the ratio of the trolley voltage and thevoltage generated by the traction motors acting as generators andprevents the braking circuit from being established while there is anymarked difference between the trolley and the regenerated voltage. Itconsists of a pivoted arm 39 which is balanced by twocores 40 and 41 oftwo solenoids 42 and a3 respectively. Solenoid 42 is energized inproportion to line voltage, while the solenoid 4:1 is energized inproportion to the regenen ated voltage. The arrangement is such that anymarked difference between the line and the regenerated voltage willcause an unbalancing which will prevent the closing of the contacts 38and consequent y prevent the closing of the circuit of the energizingcoil An overload relay lat is also provided which normally shortcircuits a resistance 45. Any excessive current, such for instance asthat due to a short circuit, will cause the relay 44 to be operated andthe resistance 15 to be inserted in the motor circuit. v

As thus' constructed and arranged, the op eration of my system is asfollows: During normal motoring operation the switch 35 will be thrownto the motoring position and the motors will be controlled in the wellunderstood manner from the master controller 12 to bring about thevarious series parallel positions. If now the train should be descendinga grade and it is desired lo conmence ,the regenerative braking, theswitch will be thrown to braking position whereupon the contactor 19will be closed and hence the armature of the generator 15 will beconnected across the fields F and the voltage of said generatorimpressedupon said fields to excite them in the same direction as during themotoring operation. When the voltage developed by the motors acting asgenerators, becomes substantially equal to line voltage the pivoted arm39 of the relay R will assume the position illustrated and the operatingcircuit of the line contactor 11 will be closed through the contacts 38and hence line contactor 11 will be closed. The motors will then act,regeneratively and deliver current to the supply line.

It may be remarked that, during the regencrating operation, theregenerated current and the exciting current for the fields F bothtraverse a circuit comprising the conductor 18, contactor 19, conductor18, the armature of generator 15, and conductor 17 and that theregenerated current is delivered to a circuit which conveys it to thetrolley T. It is understood that the master controller has been placedin an operating position, so that the motor armatures are connected inseries, series-parallel, or parallel before the switch 35 was thrown toits braking position. If it is later desirable to change the connectionsof the motor armatures to Vary the speed at which the train shall beallowed to move, then this can be effected by further operation of themaster controller 12. The current during braking is automaticallycontrolled by the automatic regulator, the operation of' which iscontrolled by the contact making ammeter, and the setting of the contactmaking ammeter is in turn determined by the position of the brakingcontroller 34:. As previously explained, the contact making ammeter inthe system illustrated in the drawing isresponsive to variations in theregenerative braking current, so that if the gcllrrent should start 'torise above a safe value due to drop in trolley voltage or iiicrease ingrade or decrease of train friction the motor operated rheostat willoperate in a manner heretofore described to insert resistnncc 20 in thefield of the generator 15 and decrease the excitation superimposed onthe fields F of the motors and thereby cause the motors which are nowacting as generators to drop a part of their load and decrease thecurrent. l n a similar manner the excitation of the series motors willbe increased by cutting out the resistance 20 from the field circuit ofthe eXciter 15 when the Various values of braking current and hencevarious braking efforts may be obtained by operating the brakingcontroller 34: which taps more or less of the resistance 33. Since thecontact making ammeter is set to balance at a. definite voltage, alarger current in the resistance or current shunt 33 will be requiredtogive a corresponding drop to operale it when part of the resistance isshort circuitcd, and the current will therefore be held constant at thishigher Value. Various braking efforts may therefore be obtained bymanipulating the braking controller 34 and the current willautomatically be kept ap proximately constant at the valuescorresponding with these braking efforts.

It will be seen that since the motor 22 is constantly operating, anysudden change of current caused by the fluctuation of the trolleyvoltage or change of grade will instantly affect the motor operatedrheostat. Hence the excitation imposed upon the series field will beaffected to bring the current back to normal. I thus-make it possible toobtain practically constant braking effort at various grades and inspite of sudden variations in voltage, this being done automaticallywithout any attention whatever from the operator. Any desired brakingeffort may be obtained by manipulating the braking controller 34c andthe current which causes this braking effort will he maintainedpractically constant within normal field limits so that the operatoralways knows just what the braking effort will be when he throws hisswitch to the braking position. .ly this arrangement it is impossible tooverload the motors and otherwise damage the apparatus due to excessivecurrent. Not only does this provide an exceedingly effective andpowerful brake upon the train which is easily controlled, but a verysubstantial saving of energy is efi'ected by returning it to the line.While this method of braking would not ordinarily be employed withoutthe usual mechanical brakes, it nevertheless makes it unnecessary to usethe mechanical brake equipment to such an extent as to wear it out sorapidly as heretofore, and a much eveuer and more effective brakingeffect is obtained at less expenses It has also been found that thetrack wear is much less with electric braking than with air brakes witha very great saving in track maintenance.

\Vhile I have described my invention as embodied in concrete form and asoperating in a specific manner in accordance with the patent statutes,it should be understood that I do not limit my invention thereto, sincevarious modifications thereof will suggest themselves to those skilledin the art Without departing from the spirit of my invention, the scopeof which is set forth in the annexed claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is

1. In combination, a dynamo-electric machine provided with an armatureand a field winding and adapted to operate either as a motor or asagenerator, a circuit, including a source of voltage which is independentof such dynamo-electric machine, adapted during the generator operationto be connected to said field winding to supply exciting current theretoand to carry both the exciting current and the-current generated by saiddyv namo-electric machine, a circuit adapted to carry only the c' rrentgenerated by said dynamo-electric machine and automatic means formaintaining the current in one of said circuits substantially constant.

2. In combination, a dynamo-electric machine provided with an armatureand a field winding and adapted to operate either as a I motor or as agenerator, a circuit, including an exciter, adapted during the generatoroperation to be connected to said field winding to supply excitingcurrent thereto and to carry both the exciting current and the currentgenerated by said dynamo-electric machine, a circuit adapted to carryonly current generated by said dynamo-electric machine, and automaticmeans for varying the voltage of said exciter and thereby maintainingthe current in one of said clrcuits substantially constant.

3. In combination, a dynamo electric-machine having a field windingconnected in series with its armature, means for giving various definitevalues of current when said dynamo electric machine is driven as agcnerator, and means whereby the regenerative current is keptsubstantially constant at any of said values re ardless of voltagefluctua tions.

4. In combination, a dyamno electric machine having a field windingconnected in series with its armature, means for giving various definitevalues of current when said dynamo electric machine is driven as agenerator, means whereby the regenerative current is kept substantiallyconstant at any of said values regardless of voltage fluctuations, andmeans whereby the circuit of said dynamo electric machine can only beclosed when there is no substantial difference between the line voltageand the voltage of the dynamo electric machine acting as a generator,

In combination, a dynamo electric machine having a field windingconnected in series with its aru'iature, a separately controllablesource of potential connected across said series field, and automaticmeans for controlling the potential supplied by said source arranged tohold the currentgenerated by said dynamo electric machine constant whenthe latter is driven as a gen-. erator.

O. In combination, a dynamo electric ma: chine having a field windingconnected in series with its armature, a separately controllable-sourccof potential connected across said series field, a power operatedrheostat for controlling the potential supplied by said source, andautomatic means for controlling said rheostat arranged .to hold thecurrent generated by said dynamo electric machine constant when thelatter is driven as a generator.

7. In combination, a. dynamo electric machine having a. field windingconnected in series with its armature, a separately controllable sourceof potential connected across said series field, a power operatedrheostat for controlling the potential supplied by said source, and acontact-making ammeter responsive to the current generated by saidse'ries wound dynamo electric machine when the latter is driven as agenerator, for controlling the extent and direction of movement of saidrheostat.

8. In combination, a dynamo electric machine having a field windingconnected in series with its armature, a separately controllable sourceof potential connected across said seiies field, a power operatedrheostat for controlling the potential supplied by said source, aresistance in series with said dynamo electric machine, and a Contactmaking ammeter inlshunt with said resistance for controlling the extentand direction arator.

9. In combinatlon, a dynamo electric machine having a field windingconnected in SGIIQS with its armature, a separately controllable sourceof potential connected across said series field, a power operatedrheostat for controlling the potential supplied by said source, anadjustable resistance in series with said dynamo electric machine, meansfor adjusting said resistance, and a contact making ammeter in shuntwith said resist ance for controlling the extent and direction ofmovement of said rheostat when said dynamo electric machine is driven asa generator. I

10. In combination, a dynamo electric machine having a fieldwindingconnected in series with its armature, a separately exciteddynamo electric machine connected across said series field winding,means for driving the latter machine as a generator, means for varyingits excitation, and automatic means for controlling said last mentionedmeans arranged to hold the current generated by said series wound dynamoelectric machine constant when the latter is driven as a generator.

11. In combination, a dynamo electric ma'- chine having a field windingconnected in series with its armature, a separately excited dynamoelectric machine connected across said series field winding, means fordriving the latter machine as a generator, means for varying itsexcitation comprising a power operated rheostat, and automatic means forcontrolling said last mentioned means arranged-to hold the currentgenerated by said series wound dynamo electric machine constant when thelatter is driven as a generator.

12. In combination, a series dynamo-electric machine, an exc1ter, meansfor connecting the armature of said exciter across the a series fieldwinding of said dynamo-electric machine, an automatic regulator forcontrolling the excitation of said exciter, and a braking controllercontrolling the operation of said automatic regulator.

13. In combination, a series dynamo-electrio machine, an exciter, meansfor connectingthe armature of saidexciter across the series fieldwinding of said dynamo-electric machine, a regulator for the excitationof saidexciter, a contact-making ammeter con trolling the'operation ofsaid regulator, and a. braking controller controlling the setting: ofsaid contact making ammeter.

14. In combination, a series dynamo-electrio machine connected to apower circuit, in

cxciter, means for connecting the armature of said e'xciter across theseries field winding of said dynamo-electric machine, a regulator forcontrolling the excitation of said exciter, a contact-making ammetercontrolling the operation of said regulator, and a braking cont-rollercontrolling the setting of said cont-act making ammeter.

15. In combination, a series dynamo-electric machine connected to apower circuit,- an' exciter, means for connecting the armature of saidexciter across the series field winding of said dynamo-electric machine,an automatic regulator for controlling the excitation of said exciter,and a braking controller controlling the' operation of said automaticregulator.

In witness whereof, I have hereunto set my hand this 29th day of July,1914.

- JESSE J. LINEBAUGH. Witnesses:

BENJAMIN B, HULL,

HELEN ORFORD.

